Abstract
Biaxial low cycle fatigue tests under pure and combined axial and torsional loading were conducted on type 316L stainless steel at room temperature, 550°C and 650°C. In the axial and combined axial-torsional loading tests, cracks propagated almost along the principal strain plane at all temperatures. But in the pure torsion test, the crack growth direction transfered from the principal strain plane to the maximum shear plane with increasing temperature. Cracks became zigzag shape at high temperature or under pure torsional loading. These differences were discussed in relation to the increase of microstructual damaged zone, such as slip band, at high temperature and the normal strain acting on crack surface. The crack length was correlated to life fraction. The crack growth behaviour varied with temperature or principal strain ratio and scattering of the data became large at an early stage of life. But this scattering became small in a latter stage of life. This suggests that microstructure of material affects the microcrack growth behaviour.
